초록
<P><B>Background</B></P><P>Polylactic acid (PLA) is one important chemical building block that is well known as a biodegradable and a biocompatible plastic. The traditional lactate fermentation processes need CaCO<SUB>3</SUB> as neutralizer to maintain the desired pH, which results in an amount of insoluble CaSO<SUB>4</SUB> waste during the purification process. To overcome such environmental issue, alkaliphilic organisms have the great potential to be used as an organic acid producer under NaOH-neutralizing agent based fermentation. Additionally, high optical purity property in <SMALL>D</SMALL>-lactic acid is now attracting more attention from both scientific and industrial communities because it can improve mechanical properties of PLA by blending <SMALL>L</SMALL>- or <SMALL>D</SMALL>-polymer together. However, the use of low-price nitrogen source for <SMALL>D</SMALL>-lactate fermentation by alkaliphilic organisms combined with NaOH-neutralizing agent based process has not been studied. Therefore, our goal was the demonstrations of newly simplify high-optical-purity <SMALL>D</SMALL>-lactate production by using low-priced peanut meal combined with non-sterile NaOH-neutralizing agent based fermentation.</P><P><B>Results</B></P><P>In this study, we developed a process for high-optical-purity <SMALL>D</SMALL>-lactate production using an engineered alkaliphilic <I>Bacillus</I> strain. First, the native <SMALL>L</SMALL>-lactate dehydrogenase gene (<I>ldh</I>) was knocked out, and the <SMALL>D</SMALL>-lactate dehydrogenase gene from <I>Lactobacillus delbrueckii</I> was introduced to construct a <SMALL>D</SMALL>-lactate producer. The key gene responsible for exopolysaccharide biosynthesis (<I>epsD</I>) was subsequently disrupted to increase the yield and simplify the downstream process. Finally, a fed-batch fermentation under non-sterile conditions was conducted using low-priced peanut meal as a nitrogen source and NaOH as a green neutralizer. The <SMALL>D</SMALL>-lactate titer reached 143.99 g/l, with a yield of 96.09 %, an overall productivity of 1.674 g/l/h including with the highest productivity at 16 h of 3.04 g/l/h, which was even higher than that of a sterile fermentation. Moreover, high optical purities (approximately 99.85 %) of <SMALL>D</SMALL>-lactate were obtained under both conditions.</P><P><B>Conclusions</B></P><P>Given the use of a cheap nitrogen source and a non-sterile green fermentation process, this study provides a more valuable and favorable fermentation process for future polymer-grade <SMALL>D</SMALL>-lactate production.</P>